1. Field of the Invention
This invention relates to a process for recovering bitumen from tar sand and, more particularly, to a low temperature, solvent extraction step followed by a water process step for recovering bitumen from tar sands contaminated with clay, the water process step including the use of a specific surface active agent to preclude contamination of the water with either bitumen residue or clay.
2. The Prior Art
The term "tar sand" refers to a consolidated mixture of bitumen (tar) and sand. Alternate names for tar sands are "oil sands" and "bituminous sands", the latter term being more technically correct in that the sense of the term provides an adequate description of the mixture. The sand constituent of tar sand is mostly alpha quartz, as determined from x-ray diffraction patterns, while the bitumen or tar constituent of the tar sands consists of a mixture of a variety of hydrocarbons and heterocyclic compounds. This bitumen, if properly separated from the sands, may be upgraded to a synthetic crude oil suitable for use as a feedstock for the production of liquid motor fuels, heating oil, and/or petrochemicals.
About 65 percent of all of the known oil in the world is contained in tar sand deposits or heavy oil deposits. Tar sand fields occur throughout the world with the exception of the continents of Australia and Antarctica. Significantly large tar sand deposits have been identified and mapped in Canada, Columbia, Trinidad-Tobago, Venezuela, and the United States. The Canadian tar sand deposits, known as the Athabasca tar sands, are located in the province of Alberta, Canada and are currently being developed. The reserves of bitumen in the Athabasca tar sands alone has been estimated to be approximately 900 billion barrels.
In the United States, approximately 24 states contain known tar sand deposits. However, about 90 to 95 percent of the mapped tar sand deposits are located within the State of Utah and are estimated to include at least 25 billion barrels of oil. While the Utah tar sand reserves appear small in comparison with the enormous potential of the Athabasca tar sands, the Utah tar sand reserves represent a significant energy resource when compared to the United States crude oil proven reserves (approximately 31.3 billion barrels) and with the United States crude oil production of almost 3.0 billion barrels during 1976. Utah tar sand deposits occur in six major locations along the eastern edge of the state with the bitumen content varying from deposit to deposit as well as within a given deposit. Current information available indicates that Utah tar sand deposits average generally less than 10 percent bitumen (by weight), although deposits have been found with a bitumen saturation of up to about 17 percent (by weight).
Athabasca tar sands and Utah tar sands are both also characterized by the presence of clay as a contaminant. The clay is finely divided and dispersed throughout the tar sand deposits, so that it represents a significant obstacle to the efficient processing of tar sands. The commercial processing of the Athabasca tar sands has created vast settling ponds where clay-contaminated water is held to allow the clay to settle. Experience has shown that the clay is so extremely fine that it remains suspended in the water for long periods. A further problem is that significant quantities of bitumen are carried into these settling ponds where it agglomerates and floats on the surface of the water to represent a pollution hazard, particularly for migratory waterfowl, and the like.
Tests have also determined that the Utah tar sands lacks connate water so that the bitumen is bonded directly to the sand grains. This bitumen is also at least one order of magnitude or at least ten times more viscous than bitumen obtained from Athabasca tar sands. Accordingly, the processing of Utah tar sands involves both displacement of the bonded bitumen from the sand grains followed by subsequent phase disengagement of the more viscous bitumen from the residual sand phase. Attempts to use conventional hot water processes that have been successfully applied to the Athabasca tar sands have been unsuccessful for processing Utah tar sands. This failure is readily apparent in light of the recognized differences in both the physical and chemical nature of the Utah tar sands.
A more comprehensive discussion of the athabasca tar sands may be found in the literature including, for example (1) E.D. Innes and J.V.D. Tear, "Canada's First Commercial Tar Sand Development," Proceedings of the Seventh World Petroleum Congress, Elsevier Publishing Co., 3, p. 633, (1967); (2) F.W. Camp, The Tar Sands of Alberta Canada, 2nd Edition, Cameron Engineering, Inc., Denver, Colo. (1974); and (3) J. Leja and C.W. Bowman, "Application of Thermodynamics to the Athabasca Tar Sands," Canadian Journal of Chemical Engineering, 46 p. 479 (1968).
Additionally, the following U.S. Patents are a few of the patents which have been granted for apparatus or processes directed toward obtaining bitumen from tar sands: U.S. Pat. Nos. 1,497,607; 1,514,113; 1,820,917; 2,871,180; 2,903,407; 2,927,007; 2,965,557; 3,159,562; 3,161,581; 3,392,105; 3,401,110; 3,553,099; 3,560,371; 3,556,980; 3,605,975; 3,784,464; 3,847,464; 3,875,046; 3,893,907; 4,096,057; 4,120,776; 4,160,720; 4,337,143; and 4,410,417. With the exception of U.S. Pat. Nos. 3,605,975, 4,120,776, and 4,160,720, each of the foregoing patents have been directed toward processing any tar sand, but, in particular, Athabasca tar sands.
From the foregoing it is clear that extensive progress has been made in separating bitumen from tar sands, particularly with regard to the Athabasca tar sands. To date no commercially feasible process has been used on the Utah tar sands other than the simple mining, crushing, and blending of the Utah tar sands into an asphalt cement which, when combined with a gravel aggregate, forms an asphalt-based concrete highly suitable for use as a paving material.
In view of the foregoing, it would be a significant advancement in the art to provide a process for recovering bitumen from clay-contaminated tar sands. An even further advancement in the art would be to recover bitumen from clay-contaminated tar sands using a readily available solvent that can be recovered and recycled. Importantly, the process should include a water process step along with the careful use of specific surface active agents to preclude contamination of the water with residual bitumen or clay. Such a novel process is disclosed and claimed herein.